Vibration sensor for fixing directly or indirectly to a vibrating component

ABSTRACT

A vibration sensor for direct or indirect mounting on a vibrating component has a housing, a pressure sleeve ( 3 ) having a central bore ( 14 ) and a piezoelectric disk ( 4 ) situated between two insulator disks ( 12 ) and two contact disks ( 9 ), ca seismic mass ( 5 ) acting on the disks by way of a spring element ( 6 ). The spring element ( 6 ) is designed with a ring shape and has a projection ( 17 ) on its inside ring area. On the outside circumference of the pressure sleeve ( 3 ) there is a recess ( 15 ) which is designed to correspond to the projection ( 17 ) and is formed to accommodate the projection ( 17 ) on the spring element ( 6 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a vibration sensor for direct orindirect mounting on a vibrating component according to the preamble ofPatent claim 1.

[0002] Vibration sensors are used, for example, as knock sensors ininternal combustion engines. European Patent 0 184 666, for example,describes such a knock sensor, which is diagramed in FIG. 4. The knocksensor has a housing 2 and a pressure sleeve 3 on whose outside arearranged a piezoceramic disk 4 and a seismic mass 5 acting on it.Seismic mass 5 acts on piezoceramic disk 4 by way of a plate spring 6.The prestress on plate spring 6 is produced by a threaded ring 7 screwedonto the pressure sleeve. Pressure sleeve 3 therefore has an outsidethread 8. The force applied to piezoceramic disk 4 may therefore beadjusted and limited as desired. Piezoceramic disk 4 is situated betweentwo contact disks 9, these contact disks 9 being connected to a cable 11by wires 10.

[0003] The arrangement described above for holding together theindividual parts of the knock sensor by way of the threaded ring and theplate spring has the disadvantages that it is relatively expensive tomanufacture and can also lead to manufacturing defects. In particular inthe manufacture of outside thread 8 on pressure sleeve 3, shavings fromcutting the thread, for example, may fall into the interspace betweenpressure sleeve 3 and piezoceramic element 4 when screwing on threadedring 8. Therefore, a short circuit may occur after the sheathing hasbeen extruded onto housing 2.

[0004] In addition, European Patent 0 184 666 describes the fastening ofplate springs 6 by using a Seeger ring.

[0005] In addition, German Patent 195 24 152 describes a vibrationsensor which has on the outside of the pressure sleeve bulges whichfunction as a stop for the plate spring. These bulges are produced bycaulking of the material of the pressure sleeve. However, inaccuraciesin the prestress of the piezoceramic disk over the plate spring mayoccur here due to uneven caulking.

ADVANTAGES OF THE INVENTION

[0006] The vibration sensor according to the present invention fordirect or indirect mounting on a vibrating component having the featuresof Patent claim 1 has the advantage over the related art that thering-shaped spring element has a projection on its inside ring area, anda recess in the pressure sleeve which corresponds to the projection isformed on the outside of the pressure sleeve. In the installed state,the recess accommodates the projection on the spring element. Therefore,the spring element is held securely by its projection in the recess inthe pressure sleeve and may thus exert a uniform prestressing force on aseismic mass or a piezoelectric disk. In addition, this also makes ispossible to eliminate the threaded ring for prestressing the springelement or other parts which are used as a stop for the spring element.In addition, it is also unnecessary to cut an outside thread in thepressure sleeve. Instead, according to the present invention, a recessmay be produced easily according to the present invention by lathing,for example. This makes production of the vibration sensor according tothe present invention especially inexpensive. Furthermore, there is norisk of any shavings falling into the interspace between thepiezoelectric disk and the pressure sleeve, which might result in ashort circuit.

[0007] The spring element and the seismic mass are preferably designedin one piece, i.e., as one part. Due to the fact that only a singlecomponent is provided, this makes it possible firstly to reduce thenumber of parts and secondly to greatly simplify assembly and shortenassembly times. Since the spring element and the seismic mass aredesigned in one piece, the seismic mass is made of the same material asthe spring element. A spring steel or the like may be used here, forexample.

[0008] In order for the seismic mass or the one-piece part in thefinished installed state to have the flattest possible contact surfacewith the insulator disks or contact disks, which are situated betweenthe seismic mass or the one-piece part and the piezoelectric disk, theseismic mass or the one-piece part is designed with a conical taper inthe relaxed state on the side facing the piezoelectric disk. In theinstalled state, this side is in flat contact; in other words, theseismic mass or the one-piece part bends like a plate spring which ispressed flatly on “block.”

[0009] The projection preferably has at least one inclined surface.Therefore, the projection may be designed so that it has a wedge shape.This makes it possible to use larger component tolerances than in therelated art for all the individual parts forming the vibration sensor.This has a very positive effect on manufacturing costs. Due to thedesign of the projection having at least one inclined surface, the bondis self-stressing in the axial direction of the vibration sensor.

[0010] The projection preferably has two inclined surfaces. Therefore,the projection may be designed so that it forms a tip which may engagein a corresponding recess having a V-shaped cross section in thepressure sleeve.

[0011] To be able to exert a sufficient prestressing force on thepiezoelectric disk, the projection of the spring element preferably hasa wedge-shaped tip having an angle of approx. 15° to approx. 120°. Thisreliably prevents the projection on the plate spring from falling out ofthe recess in the outside wall of the pressure sleeve. It is especiallypreferable for the angle here to be approximately 60°.

[0012] To provide additional security for the plate spring on thepressure sleeve, the spring element is additionally mounted on thepressure sleeve by welding. The plate spring is thus secured on thepressure sleeve by a welded joint, which may be produced by a laserwelding method or a resistance welding method, for example. In weldingthe plate spring to the pressure sleeve, it is also possible to furtherprestress the plate spring by a radial and an axial force component.

[0013] Preferably a continuous slot is formed in the spring element andin the seismic mass. In the installed state of the individual parts ofthe vibration sensor, this slot has the function of providing a flowchannel for the plastic of the housing, so that the plastic may alsoreach the inside area between the pressure sleeve and the seismic massor the piezoelectric disk with no problem. To facilitate easy threadingand thus rapid assembly of the seismic mass and the plate spring, aspacer is preferably provided in the slot before assembly to widen theparts so that they can easily be pushed onto the pressure sleeve.

[0014] In addition, at least one groove is preferably formed in the sideof the spring element facing away from the piezoelectric disk. Thisgroove also functions as a flow channel for plastic, and any desirednumber of grooves may be provided. In particular, the grooves must bepresent if there is no continuous slot in the spring element.

[0015] Thus, a vibration sensor made available according to the presentinvention is inexpensive to manufacture and easy to assemble, aprojection being provided on the spring element to engage in a recessformed on the outside of the pressure sleeve. Therefore, the projectionon the spring element may engage in the recess and thus be held inposition.

DRAWING

[0016] Two embodiments of the present invention are illustrated in thedrawing and are explained in greater detail in the followingdescription; they show:

[0017]FIG. 1 a schematic side view of a vibration sensor according to afirst embodiment of the present invention;

[0018]FIG. 2 a top view of the plate spring illustrated in FIG. 1;

[0019]FIG. 3 a schematic sectional view of a vibration sensor accordingto a second embodiment of the present invention, and

[0020]FIG. 4 a side view of a vibration sensor according to the relatedart.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0021]FIGS. 1 and 2 show a vibration sensor according to the presentinvention for direct or indirect mounting on a vibrating component (notshown) according to a first embodiment of the present invention.

[0022] As shown in FIG. 1, vibration sensor 1 according to the presentinvention has a pressure sleeve 3 which has a flange-like edge on itslower end, forming a contact surface 13 on the side facing the vibratingcomponent. In addition, pressure sleeve 3 has a central bore 14 whichaccommodates a fastening means for fastening the vibrating sensor ontothe vibrating part.

[0023] In addition, as illustrated in FIG. 1, the pressure sleeve has arecess 15 having a V-shaped cross section on its outside, the recessbeing formed on the entire outer circumference of pressure sleeve 3.

[0024] In addition, the vibration sensor according to the firstembodiment has a one-piece component 16 which functions as a seismicmass and as a spring element for applying prestress to piezoelectricdisk 4 at the same time. As illustrated in FIG. 1, component 16 includesa wedge-shaped projection 17 which is formed on the upper insideperipheral ring of component 16. Wedge-shaped projection 17 engages inrecess 15 formed in pressure sleeve 3. FIG. 1 shows component 16 beforeassembly with dotted lines and just prior to the final installedposition with solid lines. Component 16 moves here in the direction ofarrow A into the final assembly position. In the final position, theinclined surfaces of projection 17 are in direct contact with theinclined surfaces of recess 15. Therefore, recess 15 functions as a stopfor projection 17 and thus determines the prestress acting onpiezoelectric disk 4. In the final installed position, the bottom sideof one-piece component 16 lies flat on insulator disk 12.

[0025] As illustrated in FIG. 1, component 16 acts on piezoelectric disk4 by way of an insulator disk 12 and a contact disk 9. Piezoelectricdisk 4 is in turn arranged in contact with the flange-like projection onpressure sleeve 3 by way of a contact disk 9 and an insulator disk 12.

[0026]FIG. 2 shows a top view of component 16 which forms the springelement and the seismic mass. As shown in FIG. 2, a continuous slot 18is provided in component 16. Therefore, projection 17 is not completelyring shaped. In addition, two grooves 19 and 20 are provided in theupper area of component 16. These grooves function as flow channels fora plastic which is molded around the preassembled individual parts as ahousing (not shown) after preassembly of the individual parts, so thatplastic can also reach between component 16 and piezoelectric disk 4 andthe cylindrical area of pressure sleeve 3. Slot 18 also has the samefunction as grooves 19 and 20, forming a broad passage for the injectionmolding plastic. In addition, slot 18 simplifies placement of component16 over pressure sleeve 3, because component 16 can then be widenedeasily and easily pushed over pressure sleeve 3. A spacer is preferablyarranged in slot 18 before assembly to hold component 16 in the widenedstate.

[0027]FIG. 3 shows a second embodiment according to the presentinvention. The same or similar parts are designated with the samereference notation as in the first embodiment and are therefore notdescribed in detail below.

[0028] In contrast with the first embodiment, a one-piece component isno longer provided for the seismic mass and the plate spring in thesecond embodiment, but instead two separate components are provided,namely a seismic mass 5 and a plate spring 6. As shown in FIG. 3,seismic mass 5 is designed as a ring-shaped disk in the known manner. Onits inside circumferential area, plate spring 6 has a projection 17shaped like a wedge. As shown in FIG. 3, projection 17 has two inclinedsurfaces which in the installed state engage in a V-shaped recess 15 onthe outside of pressure sleeve 3. Therefore, plate spring 6 exerts aprestress on seismic mass 5 and piezoelectric disk 4. The additionalcomponents of the vibration sensor according to the second embodimentcorrespond to those in the first embodiment and therefore will not bedescribed in detail below.

[0029] In addition, it is possible with both embodiments for component16 or plate spring 6 to additionally be mounted on pressure sleeve 3 bya weld to increase the long-term stability of the vibration sensor. Thisis indicated with arrows B in FIG. 1. In addition, it is also possiblein the welding operation for an additional prestress to be applied tocomponent 16 or spring element 6 by a radial force component and anaxial force component.

[0030] In summary, the present invention relates to a vibration sensorfor direct or indirect mounting on a vibrating component, having ahousing, a pressure sleeve 3 with a central bore 14 and a piezoelectricdisk 4 situated between two insulator disks 12 and two contact disks 9on which a seismic mass 5 acts by way of a spring element 6. Springelement 6 is designed with a ring shape and has a projection 17 on itsinside ring area. A recess 15 which is designed to match the projectionis formed on the outside circumference of pressure sleeve 3 to receiveprojection 17 of spring element 6.

[0031] The previous description of the embodiments according to thepresent invention is given only for illustrative purposes and not forthe purpose of restricting the scope of the present invention. Variouschanges and modifications are possible within the scope of the presentinvention without going beyond the scope of the present invention or itsequivalents.

What is claimed is:
 1. A vibration sensor for direct or indirectmounting on a vibrating component, having a pressure sleeve (3) having acentral bore (14) and a piezoelectric disk (4), situated between twoinsulator disks (12) and two contact disks (9), upon which a seismicmass (5) acts via a spring element (6), wherein the spring element (6)is designed with a ring shape and has a projection (17) on its insidering area, and a recess (15) which is designed to correspond to theprojection (17) is formed on the outside circumference of the pressuresleeve (3) to accommodate the projection (17) on the spring element (6).2. The vibration sensor according to claim 1, wherein the spring elementand the seismic mass are designed as a one-piece part (16).
 3. Thevibration sensor according to claim 1 or 2, wherein the seismic mass (5)is designed with a conical taper in the relaxed state on the side facingthe piezoelectric disk (4).
 4. The vibration sensor according to one ofclaims 1 through 3, wherein the projection (17) has at least oneinclined surface.
 5. The vibration sensor according to claim 4, whereinthe projection (17) has two inclined surfaces.
 6. The vibration sensoraccording to claim 4 or 5, wherein the projection (17) has awedge-shaped tip having an angle of approx. 15° to 120°.
 7. Thevibration sensor according to one of claims 1 through 6, wherein acontinuous slot (18) is formed in the spring element (6) and the seismicmass (5) or in the one-piece component (16).
 8. The vibration sensoraccording to one of claims 1 through 7, wherein at least one groove (19,20) is formed in the side of the spring element (6) facing away from thepiezoelectric disk (4), said groove being formed from the outsidecircumference to the inside circumference.
 9. The vibration sensoraccording to claim 7 or 8, wherein before assembly, a spacer is providedin the slot (18) in the spring element (16) and/or the seismic mass (5)or the one-piece component (16) to make possible their being simple slidonto the pressure sleeve (3).
 10. The vibration sensor according to oneof claims 1 through 9, wherein the projection (17) is additionallyfastened on the pressure sleeve (3) by welding.